Biocompatible polymer and filter for selectively eliminating leucocytes using the same

ABSTRACT

It is intended to provide a polymer which is scarcely eluted, has a high biocompatibility and is useful in a filter for selectively eliminating leucocytes. It is also intended to provide a filter for selectively eliminating leucocytes, a filtration apparatus for selectively eliminating leucocytes and a system for selectively eliminating leucocytes, each having the above-described polymer. The above objects can be achieved by providing a polymer which comprises from 8% by mol to 45% by mol of a unit originating in a polymerizable monomer having a polyalkylene oxide chain, from 30% by mol to 90% by mol of a unit originating in a polymerizable monomer having a hydrophobic group, and from 2% by mol to 50% by mol of a unit originating in polymerizable monomer having a hydroxyl group.

TECHNICAL FIELD

The present invention relates to a polymer having excellentbiocompatibility. More particularly, the present invention relates to apolymer that can be used for a filter for selectively removingleukocytes which exhibits only slight adherence with platelets and canselectively remove leukocytes from blood. The present invention alsorelates to a filter material for selectively removing leukocytes inblood during transfusion or extracorporeal circulation, an apparatus forselectively removing leukocytes, a system for selectively removingleukocytes, and a method of treating diseases using the system.

BACKGROUND ART

Following the progress of immunology and blood transfusion in recentyears, component transfusion in which only blood components required fortreating various diseases are transfused has become more popular thanconventional whole blood transfusion. Blood component transfusion is anoutstanding transfusion treatment exhibiting a high curative effect,while mitigating the load on patients during transfusion. Various bloodpreparations used for the blood component transfusion, such asconcentrated erythrocytes, concentrated platelets, and platelet poorplasma, are prepared by centrifuging whole blood obtained by donation.However, it has become known that side reactions are induced aftertransfusion due to the leukocytes contained in these blood preparationsbecause the blood preparations obtained by centrifugation contain manyleukocytes. The side reactions after transfusion include comparativelyslight side reactions, such as headache, nausea, a chill, and anon-hemolytic exothermic reaction, as well as serious side reactionssuch as induction of graft versus host (GVH) reaction to a patient withan immune disorder in which the transfused leukocytes has adeath-inducing effect on the skin and internal organs of the recipient,infection by viruses present in leukocytes such as cytomegalovirusinfection, and alloantigen sensibilization. Removing leukocytes from theblood preparations is effective in preventing such side reactions aftertransfusion.

There has been an increasing demand for the technology of removingleukocytes from patient's peripheral blood for medical treatment ofsystemic erythematodes, chronic or malignant rheumatoid arthritis,Behcet's disease, idiopathic thrombo-cytopenic purpura, autoimmunehepatitis, chronic ulcerative colitis, Crohn's disease, atopicdermatitis, rapidly progressive glomerulonephritis, and systemicinflammatory response syndrome, and for the purpose of immunesuppression before transplant. Leukocyte removal is practiced also inthe field of heart surgery, wherein leukocytes are removed from theblood perfused after coronary-artery bypass surgery to mitigate ahindrance effect by activated leukocytes.

Methods for removing leukocytes from blood are broadly classified into acentrifuge separation method, making use of differences in the specificgravity of blood components, and a filter method using a fibrous mediumsuch as non-woven fabric or a porous sponge-like material havingthree-dimensional continuous pore networks as a filter. The filtermethod is more popular due to higher leukocyte removal efficiency,simple procedure, and lower cost.

Polymer materials consisting these leukocyte-removal filters aregenerally hydrophobic and cause other useful blood components such asplatelets to adhere when removing leukocytes. It has been difficult toachieve a balance between the leukocyte-removal efficiency and theplatelet recovery efficiency. Development of a material that canselectively remove leukocytes, while allowing platelets to pass through,has been strongly desired, particularly for patients with a disease, inwhich a decrease in platelets is undesirable, such as idiopathicthrombocytopenic purpura or autoimmune hepatitis.

When an aqueous-type liquid containing platelets such as blood is causedto come in contact with a material, the higher the hydrophilicity of thesurface of the material, the more difficult it is for the platelets tobecome activated and the easier it is for a water layer to be formed onthe material surface by the hydrogen bond of water and the material,whereby adsorption of platelets and hydrophobic proteins can beinhibited. Therefore, various hydrophilic polymers have been developedto modify the surface of materials and methods for introducing suchpolymers onto the surface of materials by graft polymerization orcoating are known in the art. JP-A 2000-245833 discloses a filtermaterial for selectively removing leukocytes. The material allowserythrocytes and platelets to pass through, but does not allowleukocytes to pass through. In the filter material, the above problemshave been overcome by coating a hydrophilic polymer onto the materialforming the filter. One possible problem with the coated filter materialis elution of the hydrophilic polymer from the surface. Although thepossibility of the polymer elution into an aqueous solution is very low,a material with a smaller risk of elution has been desired for use inprocessing of a large amount of blood, such as that used forextracorporeal circulation, to ensure stability of the filter materialwhen it is kept in contact with an aqueous solution such as blood for along time.

JP-A 07-25776 discloses a filter material coated with a polymer havingboth hydrophobic groups and hydrophilic polyethylene oxide chains. Thisis a filter material with a reduced risk of polymer elution bydecreasing the solubility of the polymer in an aqueous solution byintroducing hydrophobic groups into the polymer. However, since thepolymer has both hydrophobic groups and hydrophilic groups havingopposite properties each other in the polymer molecule, the action ofhydrophobic portions through which the polymer is caused to adhere tothe filter supporting body which consists the filter material isreduced. It has, therefore, been difficult to ensure a balance betweenfilter performance and elution properties using this technology alone.The inventors of the present invention examined this technology using apolymer made from methyl methacrylate and methoxypoly(ethylene glycolmethacrylate) having polyethylene oxide chains. As a result, the presentinventors have found that aqueous solutions become turbid due to polymerelution.

The present inventors have further found that a specific removingmaterial surface can absorb viruses, remove leukocytes, and recoverplatelets and filed a patent application on the invention covering thisfinding (PCT/JP 02/10766, WO 03/033035). Although this prior patentapplication describes the same polymer as the polymer of the presentinvention as an example of the polymer for forming a specific surface,the prior invention differs from the present invention in that theclaimed filter removes viruses simultaneously with leukocytes. Inaddition, the inventors of the present invention coated a specificsupporting body with the polymer described in the prior application asone embodiment, of which the conditions of polymerization andpurification differ from those applied to the present invention, andevaluated elution of the polymer. As a result, the present inventorshave found that a slight degree of elution occurred, although the degreewas not so remarkable as to cause the test solution to become turbid. Itis needless to mention that it is more desirable to further suppress theelution taking into consideration the application of the filter in amedical treatment.

There have been no high performance polymers used for filters forselective removal of leukocytes exhibiting both high safety and highblood filtration performance at the same time.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a novel polymer havingan extremely low elution property and excellent biocompatibility, usefulas a filter for selective removal of leukocytes which can selectivelyremove leukocytes from various bloods, particularly from whole blood,while preventing adsorption of platelets as much as possible.Specifically, the present invention provides a novel polymer that can beeffectively used for platelet transfusion or extracorporeal circulationfor leukocyte removal, excelling in biocompatibility, exhibiting only alow adsorption to platelets, and having a low elution property.

Other objects of the present invention are to provide a filter materialfor selective removal of leukocytes, a filter apparatus for selectiveremoval of leukocytes, and a system for selective removal of leukocytesusing the above polymer.

As a result of extensive studies, the present inventors have found thata polymer comprising a unit originating from a polymerizable monomerhaving a polyalkylene oxide chain, a unit originating from apolymerizable monomer having a hydrophobic group, and a unit originatingfrom a polymerizable monomer having a hydroxyl group at a specific ratiosurprisingly exhibits remarkably low elution property, excellentbiocompatibility, particularly low adsorption to platelets, andexcellent selective leukocyte removal capability. This finding has ledto the completion of the present invention.

Specifically, the present invention provides a biocompatible polymercomprising 8-45 mol % of a unit originating from a polymerizable monomerhaving a polyalkylene oxide chain, 30-90 mol % of a unit originatingfrom a polymerizable monomer having a hydrophobic group, and 2-50 mol %of a unit originating from a polymerizable monomer having a hydroxylgroup, wherein the total of the three types of monomer units is 100 mol%.

In the present invention, a more excellent elution property has beenconfirmed to be obtained if the weight average molecular weight of thepolymer is in the range from 100,000 to 3,000,000.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of the leukocyte-removal filterapparatus of the present invention.

FIG. 2 is a schematic drawing showing one embodiment of the system forselective leukocyte removal of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The polyalkylene oxide chain used in the present invention refers to arepeating structure in which an alkyl group and an oxygen atom bondalternately. The polyalkylene oxide chains with an alkyl group having2-4 carbon atoms, such as a polyethylene oxide chain, polypropyleneoxide chain, and polybutylene oxide chain, are preferable. Thepolyalkylene oxide chain in the polymer exhibits a high plateletadsorption preventing effect due to the outstanding compatibility withblood possessed by the polyalkylene oxide chain.

The repeating number of the alkylene oxide chain used in the presentinvention is preferably from 2 to 10. If the number of repetitions isless than 2, it is difficult to obtain a sufficient platelet adsorptionpreventing effect. If the number of repetitions is more than 10, thepolymer becomes less adhesive to the filter supporting body, therebyincreasing a tendency of the polymer eluting more easily. The number ofrepetitions is preferably 2 to 6, and more preferably 2 to 4.

Examples of the polymerizable monomer having the polyalkylene oxidechain include, but are not limited to, methoxydiethylene glycol(meth)acrylate, ethoxydiethylene glycol (meth)acrylate,methoxydipropylene glycol (meth)acrylate, ethoxydipropylene glycol(meth)acrylate, methoxytriethylene glycol (meth)acrylate,methoxytripropylene glycol (meth) acrylate, ethoxytriethylene glycol(meth)acrylate, ethoxytripropylene glycol (meth)acrylate,methoxytetraethylene glycol (meth)acrylate, methoxytetrapropylene glycol(meth)acrylate, ethoxytetraethylene glycol (meth)acrylate,thoxytetrapropylene glycol (meth)acrylate, ethoxydiethylene glycol vinylether, ethoxydiethylene glycol vinyl ether, methoxytriethylene glycolvinyl ether, and ethoxytriethylene glycol vinyl ether. Of these,(meth)acrylate having a polyethylene glycol chain such asmethoxydiethylene glycol (meth)acrylate, ethoxydiethylene glycol(meth)acrylate, methoxytriethylene glycol (meth)acrylate,ethoxytriethylene glycol (meth)acrylate, methoxytetraethylene glycol(meth)acrylate, and ethoxytetraethylene glycol (meth) acrylate arepreferably used due to the high platelet adsorption preventing effect.Methoxydiethylene glycol (meth)acrylate is most preferable from theviewpoint of easy availability, easy handling, easy polymerization, andthe like. The (meth)acrylate in the present invention refers to acrylateor methacrylate, or both.

It is necessary for the polymer of the present invention to contain theunit originating from the polymerizable monomer having a polyalkyleneoxide chain in an amount from 8 mol % to 45 mol %. If less than 8 mol %,the platelet adsorption preventing effect of the polyalkylene oxidechain is insufficient, resulting in reduced platelet recoveryperformance. If more than 45 mol %, the hydrophobicity of the polymerdecreases, giving rise to easy elution of the polymer when coming intocontact with an aqueous solution such as blood. The amount of the unitis preferably from 20 mol % to 40 mol %, and more preferably from 25 mol% to 35 mol %.

The term “unit” in the present invention refers to a minimum recurringunit in a polymer molecule originating from respective polymerizablemonomers. For example, in the case of the addition polymerization of apolymerizable monomer of a vinyl compound with the formula CH₂—CXY(wherein X is H or a substituent other than H and Y is a substituentother than X) by simply opening the double bond, the minimum recurringunit is —(CH₂—CXY)—. In the case where the polymer is synthesized bypolycondensation from a polymer precursor of the formula A-(R)-B,wherein R indicates a part not released in the polymerization and A andB are releasable parts during the polymerization reaction, —(R)— is theminimum recurring unit.

The term “polymerizable monomer having a hydrophobic group” in thepresent invention refers to a polymerizable monomer having solubility inwater at 20° C. of 0 wt % or more and less than 50 wt %, and notcontaining a polyalkylene oxide chain and a hydroxyl group in themolecule. The unit originating from a polymerizable monomer having ahydrophobic group has effects of decreasing the solubility of thepolymer in an aqueous solution, preventing elution of the polymer, andincreasing leukocyte removal performance.

The solubility can be determined by a known method such as a dew pointmethod, thermal analysis, electric method comprising measurement of theelectromotive force or electric conductivity of the solution, gaschromatography analysis, and tracer method in the case where the monomeris a solid. When the monomer is a liquid, the solubility can bedetermined by, in addition to the methods applied to a solid monomer, acapacitance method, light scattering method, vapor pressure method, orthe like, all of which are known in the art. As simpler method, when themonomer has a boiling point sufficiently higher than the boiling pointof water, a method of vaporizing water from a saturated solution of themonomer and measuring the weight of the residue can be used.

As examples of the above-mentioned polymerizable monomer having ahydrophobic group, styrene, methylstyrene, butyl (meth)acrylate,isobutyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, ethyl (meth)acrylate, methyl (meth)acrylate, phenyl(meth)acrylate, ethylhexyl (meth) acrylate, and vinyl acetate can begiven. Of these, alkyl (meth)acrylates such as butyl (meth)acrylate,isobutyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, ethyl (meth)acrylate, and methyl (meth)acrylate arepreferably used due to their adequately hydrophobic and easilypolymerizable properties. Methyl (meth)acrylate is most preferable fromthe viewpoint of high biological safety.

It is necessary for the polymer of the present invention to contain theunit originating from the polymerizable monomer having a hydrophobicgroup in an amount from 30 mol % to 90 mol %. If less than 30 mol %, thehydrophobicity of the polymer decreases, giving rise to easy elution ofthe polymer when coming into contact with an aqueous solution such asblood. If more than 90 mol %, the hydrophobicity of the polymerincreases, giving rise to increased adsorption of platelets to thesurface of the filter material. The amount of the unit is preferablyfrom 35 mol % to 80 mol %, and more preferably from 40 mol % to 70 mol%.

The term “polymerizable monomer containing a hydroxyl group” as used inthe present invention refers to a polymerizable monomer having ahydroxyl group, but not containing a polyalkylene oxide chain in themolecule. For example, polymerizable monomers containing an alkylhydroxyl group such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl(meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxyisobutyl(meth)acrylate, 3-hydroxyisobutyl (meth)acrylate, 2-hydroxybutyl(meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl(meth)acrylate are preferably used.

It is necessary for the polymer of the present invention to contain theunit originating from the polymerizable monomer having a hydroxyl groupin an amount from 2 mol % to 50 mol %. If less than 2 mol %, thehydrophilicity of the polymer decreases, giving rise to increasedadsorption of platelets to the surface of the filter material. If morethan 50 mol %, the hydrophobicity of the polymer decreases, giving riseto easy elution of the polymer when coming into contact with an aqueoussolution such as blood. The amount of the unit is preferably from 5 mol% to 40 mol %, and more preferably from 10 mol % to 30 mol %.

The content ratio of the unit originating from the polymerizable monomerhaving a hydroxyl group to the unit originating from the polymerizablemonomer having a hydrophobic group in the polymer of the presentinvention is preferably from 0.05 to 1. The content ratio in the presentinvention is a value obtained by dividing the mol content of the unitoriginating from the polymerizable monomer having a hydroxyl group bythe mol content of the unit originating from the polymerizable monomerhaving a hydrophobic group in the polymer. If the content ratio is lessthan 0.05, the hydrophilicity provided by hydroxyl groups is canceled byhydrophobic groups and the hydrophilicity of the polymer decreases,giving rise to increased adsorption of platelets to the surface of thefilter material. If more than 1, the elution preventive effect of thehydrophobic groups is canceled by hydroxyl groups and hydrophobicity ofthe polymer decreases, giving rise to easy elution of the polymer whencoming into contact with an aqueous solution such as blood. The contentratio is preferably from 0.1 to 0.9, and more preferably from 0.15 to0.8.

The polymerizable monomer having a hydroxyl group used in the polymer ofthe present invention preferably has solubility in water at 20° C. inthe range from 3 wt % or more, but less than 50 wt %. Due to themoderate hydrophilic and hydrophobic properties, the polymerizablemonomer having a hydroxyl group provides the polymer with the effect ofpreventing adsorption of platelets and hydrophobic proteins togetherwith the polyalkylene oxide chain, and, at the same time, the effect ofpreventing elution of the polymer together with a unit originating fromstrong hydrophobic polymerizable monomers. As the polymerizable monomercontaining a hydroxyl group and having the above-mentioned solubility,2-hydroxypropyl (meth)acrylate and 2-hydroxyisobutyl (meth)acrylate arepreferably used due to their moderate hydrophilic and hydrophobicproperties. Of these, 2-hydroxyisobutyl (meth)acrylate is mostpreferable from the viewpoint of the moderate hydrophilic properties.

The chemical composition of a polymer can be determined by extractingthe polymer using an appropriate solvent which does not dissolve thesupporting body of the filter and analyzing the extract by a knownmethod such as NMR spectrum, IR spectrum, and elemental analysis. Whenthe polymer is not dissolved, in addition to the above-mentionedmethods, known surface analytical methods such as X-ray photoelectronspectroscopy (ESCA) and a method of using an electron probe X-raymicroanalyser (EPMA) can be used.

The polymer of the present invention preferably has a weight averagemolecular weight (Mw) in the range of 100,000 to 3,000,000. If the Mw isless than 100,000, the molecular weight of the polymer decreases whenthe polymer is sterilized, particularly by radiation, giving rise to anincrease in the eluted amount. If the weight average molecular weight(Mw) is more than 3,000,000, solubility of the polymer in the solventused for coating decreases. In addition, there may be the case where thepolymer cannot be produced in a stable manner. The Mw is more preferablyfrom 150,000 to 2,000,000, and most preferably from 200,000 to1,500,000. Although the Mw can be determined by various known methods, avalue determined by gel permeation chromatography (hereinafterabbreviated to GPC) using polymethyl methacrylate as a standard was usedin the present invention.

The polymer may be either a random copolymer or a block copolymer. Therandom copolymer is, however, more preferable since the block copolymermay have a tendency of decreasing the solubility in a solvent when usedfor coating and may have a tendency of impairing coating uniformity dueto micelle formation in the solution. As the form of the polymermolecule chain, a linear polymer is more preferable since a branchedpolymer may have a tendency of decreasing the solubility in a solventwhen used for coating and may have a tendency of impairing coatinguniformity due to micelle formation in the solution.

The polymer of the present invention is preferably a nonionic-typepolymer. The term “nonionic” refers to the properties of the polymerneither anionized nor cationized by blood or body fluid around theneutral pH, and containing neither a negatively charged functional groupsuch as a carboxylic acid group, sulfonic group, phosphate group, andphenol group nor a positively charged functional group such as a primaryamino group, secondary amino group, tertiary amino group, quaternaryammonium group, pyridyl group, and imidazoyl group in the molecule.

The blood clotting factor XII is said to be activated and cause a chainreaction in the clotting system on a negatively charged materialsurface. A positively charged material surface, on the other hand, tendsto adsorb blood cells such as erythrocytes, platelets, and leukocytesdue to the electrostatic interaction with the negative charge on thecell surface. JP-A 06-51060 discloses a technology for removingleukocytes more efficiently while preventing platelet adsorption byproviding a slightly positively charged surface. However, electrostaticinteraction is not desirable, because high platelet recovery performanceis necessary for processing a large amount of blood. When the polymer isnonionic, the clotting system is activated only slightly so that stableplatelet recovery performance can be attained even if the polymer isused for large scale blood treatment such as extracorporeal circulation.

A common polymerization method can be employed for synthesizing thepolymer of the present invention. Addition polymerization (vinylpolymerization) and the like involving chain reactions; isomerizationpolymerization; and dissociation reaction, polyaddition,polycondensation, addition polycondensation, and the like involvingconsecutive reactions may be employed. Radicals, ions, and the like canbe used as chain carriers in producing the polymer.

As the type of polymerization, solution polymerization, masspolymerization, deposition polymerization, emulsion polymerization, andthe like can be given. Of these, solution polymerization is preferable.An example of the polymerization method is given below. An ethanolsolution in which each monomer or a diazo initiator is dissolved isadded dropwise to ethanol used as a polymerization solvent whilestirring at a constant temperature below the boiling point of ethanol ina nitrogen atmosphere. A stabilizer and the like may be added asappropriate. The reaction yield is measured and confirmed by using aknown method such as gas chromatography.

The reaction product may be purified by a common chemical purificationmethod to remove impurities such as low molecular weight components andunreacted materials which are contained in the polymer or the reactionsolution containing the polymer. As the purification method, a methodcomprising dissolving the reaction mixture in a solvent that dissolvesthe impurities, but does not dissolve the polymer, to cause the polymerto precipitate, and separating the precipitate (polymer) by filtration,decantation, or the like can be given. As required, the precipitate iswashed with a solvent with solubility slightly higher than that of theprecipitation solvent (a mixture of the precipitation solvent and asolvent, for example) and the precipitate is dried under reducedpressure until the weight of the precipitate becomes constant, therebyobtaining a solid polymer.

The polymer of the present invention can be suitably used for thesurfaces of medical maetrials, because the polymer can increase thebiocompatibility of a medical material when coated on the surface. Forexample, the polymer can be used for artificial organs such as anartificial blood vessel, artificial kidney, and artificial liver, bloodcell separation filters such as a leukocyte removal filter, dialysismembrane, anti-thrombus material, and the like. In particular, since thepolymer can selectively remove leukocytes from blood, that is, aconcentrated erythrocyte preparation, concentrated platelet preparation,platelet poor plasma preparation, peripheral blood, cell floatingsolutions containing leukocytes and platelets such as lymph and marrowfluid, the polymer can be suitably used as a selective leukocyte removalfilter of blood preparations and a selective leukocyte removing filterfor extracorporeal circulation. In addition, since the polymer is elutedonly with difficulty and is stable even if caused to be in contact withan aqueous solution for a long period of time, the polymer can be mostsuitably used for selective leukocyte removal apparatus forextracorporeal circulation designed to process a large amount of blood.

The present invention also provides a filter material for selectiveremoval of leukocytes characterized by having the biocompatible polymerof the present invention present at least on the surface of the filtersupporting body. The term “having the polymer present at least on thesurface of the supporting material” indicates the polymer is present onthe surface of the supporting material substantially covering thesurface. As the method for having the polymer present on the surface offilter, known methods such as a method of coating or depositing andinsolubilizing the polymer on the supporting body of the filter, amethod of phase-separating the polymer from the supporting body of thefilter during fabrication, and the like can be used. Of these, themethod of coating is most preferable due to the easy industrialapplicability and excellent performance stability.

Since the polymer used for the filter material for selectively removingleukocytes of the present invention comes into contact with body fluidssuch as blood, it is desirable that the polymer has extremely lowsolubility in water. To prevent detachment of the polymer from thefilter supporting material, it is desirable that the polymer has highadsorption with filter supporting material. As the index for solubilityof the polymer in water and adsorption of the polymer with the filtersupporting body, the δ-value of the solubility parameter described in J.H. Hildebrand and R. L. Scott, The Solubility of Nonelectrolytes, 3rded. (Dover Pub., New York) can be used. In general, the closer theδ-value of two substances, the stronger the adsorption and the higherthe solubility of the two substances. Therefore, the polymer used forthe filter material for selectively removing leukocytes of the presentinvention should preferably have a δ-value that differs largely from theδ-value (23.3) of water and is close to the δ-value of the filtersupporting body. A combination of the polymer having a δ-value in therange from 10.0 to 11.5 and the filter supporting body having theδ-value of in the range from 7.0 to 15.0 can produce a filter materialwith extremely low solubility in water without a risk of detachment ofthe polymer from the filter supporting body. A more preferablecombination is the polymer's δ-value of 10.0 to 10.8 and the filtersupporting body's δ-value of 7.2 to 14.5, and a still more preferablecombination is the polymer's δ-value of 10.0 to 10.5 and the filtersupporting body's δ-value of 7.5 to 14.0.

The δ-values can be calculated according to the following formula (1)which is described in the above document:δ=(E/V)^(1/2)  (1)wherein E is cohesive energy (cal mol⁻¹) and V is molar volume (cm³mol⁻¹).

The Adhesion Handbook, Second Edition, edited by The Adhesion Society ofJapan (THE NIKKAN KOGYO SHIMBUN, LTD.) describes δ-values of solventsand polymers measured heretofore. These values can be used. When thevalues E and V in the formula (1) are unknown, the δ-values can becalculated from the molecular structure according to the Fedors methoddescribed in Kozo Shinoda, Solution and Solubility, Maruzen Co., Ltd.Using the Fedors method, the e (cohesive energy (cal mol⁻¹)) values andthe v (molar volume (cm³ mol⁻¹)) values that have been calculated by theFedors for various structural units of compounds are integrated todetermine the E value and V value of the compound. The δ-value of thecompound is then calculated using the E value and V value. The resultingδ-value is very close to the measured value.

Any material having a δ-value of the above range and not damaging bloodcells can be used as the filter supporting body for the filter materialfor selectively removing leukocytes of the present invention withoutspecific limitations. As examples of such a material, polyester,polyolefin, polyacrylonitrile, polyamide, polystyrene, polyalkyl(meth)acrylate, polyvinyl chloride, polychloroprene, polyurethane,polyvinyl alcohol, polyvinyl acetate, polysulfone, polyether sulfone,polybutadiene, butadiene-acrylonitrile copolymer, styrene-butadienecopolymer, ethylene-vinyl alcohol copolymer, cellulose diacetate, andethyl cellulose can be given. Of these, polyester and polyolefin arepreferable, with a particularly preferable organic filter material beingpolyester.

Various methods can be used for coating the polymer onto the filtersupporting body without any specific limitations inasmuch as the surfaceof the filter supporting body can be coated with a certain degree ofuniformity without unduly clogging the pores in the filter supportingbody. Examples of the method for coating the polymer onto the filtersupporting body include, but are not limited to, a method ofimpregnating the filter supporting body with a polymer solution, amethod of spraying the polymer solution to the filter supporting body,and a method of applying or transcribing the polymer solution to thefilter supporting body using a rotogravure roll or the like. Of thesemethods, the method of impregnating the filter supporting body with apolymer solution and the method of applying or transcribing the polymersolution to the filter supporting body using a rotogravure roll arepreferable due to the excellent continuous productivity and low cost.

Various solvents that do not dissolve the filter supporting body to anoticeable degree can be used as the solvent to dissolve the polymer inthe coating operation without any specific limitations. Examples of sucha solvent include, but are not limited to, water and aqueous solutionscontaining an inorganic salt, alcohols such as methanol, ethanol,propanol, and butanol, ketones such as acetone and methyl ethyl ketone,esters such as methyl acetate and ethyl acetate, hydrocarbons such asbenzene and cyclohexane, halogenated hydrocarbons such as chloroform anddichloromethane, sulfur-containing solvents such as dimethyl sulfoxide,amides such as dimethylformamide and dimethylacetamide, and mixtures oftwo or more of the above solvents to the extent possible.

The concentration of the polymer solution used for coating is preferably0.001 wt % or more, but less than 10 wt %. If the concentration is lessthan 0.001 wt %, the amount of the polymer on the surface is too smallfor the filter material to exhibit sufficient biocompatibility such asproperties of preventing platelet adsorption. If the concentration is 10wt % or more, on the other hand, not only does the solution have toogreat a viscosity to be handled with ease, but also the surfaceproperties of the medical material may be significantly affected. Inaddition, such a high concentration is too expensive to be efficientlyused. For these reasons, the polymer concentration is more preferably0.005 wt % or more, but less than 7 wt %, and most preferably 0.01 wt %or more, but less than 5 wt %. The amount of the polymer held on thefilter supporting material is preferably 0.001 wt % or more, but lessthan 10 wt %. If less than 0.001 wt %, the amount of the polymer on thesurface is too small for the filter material to exhibit sufficientbiocompatibility such as properties of preventing platelet adsorption.If 10 wt % or more, the amount of the polymer is excessive, giving riseto easy elution of the polymer when the filter material comes intocontact with an aqueous solution such as blood. Amore preferable amountof the polymer is 0.005 wt % or more, but less than 7 wt %, with theamount of 0.01 wt % or more, but less than 5 wt % being most preferable.

To dry the polymer solution after coating, a method comprising removingexcess solvent by mechanical compression, by gravity, or by injectinggas such as air or nitrogen, and treating the coated material in dry airor under reduced pressure at atmospheric temperature or with heating canbe employed. Adsorption of the polymer to the filter supporting body maybe further increased by a heat treatment after coating the polymer or bypost processing of irradiating the coated surface with γ-rays, electronbeams, or the like. The coating operation may be carried out eitherduring manufacturing the filter supporting body or after manufacturingthe filter supporting body.

The polymer coating rate in the entire surface of the leukocyte removalfilter material of the present invention is preferably from 40% to 90%.The coating rate in the present invention refers to the proportion ofthe area covered with the polymer in the entire surface area of thefilter supporting body. If the coating rate is less than 40 wt %, theamount of the polymer on the surface is too small for the filtermaterial to exhibit sufficient biocompatibility such as properties ofrejecting platelet adsorption. If 90 wt % or more, the amount of thepolymer is excessive, giving rise to easy elution of the polymer whenthe filter material comes into contact with an aqueous solution such asblood. Amore preferable range of coating rate is from 45% to 85%, with astill more preferable range being from 50% to 80%.

The coating rate can be determined using an analyzer commonly used toanalyze polarized surfaces such as an XPS (X-ray PhotoelectronSpectroscopy) analyzer or a TOF-SIMS (Time Of Flight-Secondary Ion MassSpectrometry) analyzer. When two or more analytical methods can be usedfor measuring the surface coating rate, the value obtained using the XPSand the like in which method the information at the depth from severaltens to one hundred A (angstrom) from the surface is deemed to becorrect, but when the surface properties permits only measurement of thecoating rate by the SIMS method or the like, the value obtained usingone of these methods is regarded to be correct.

The method of measuring the coating rate will now be described in moredetail by way of a specific example.

In the case of a filter material prepared by coating a filter supportingbody of polyethylene terephthalate nonwoven fabric with a polymer madefrom three polymerizable monomers (methoxydiethylene glycolmethacrylate, methyl methacrylate, and 2-hydroxyisobutyl methacrylate),the coating rate can be determined as follows.

Cls spectra of the filter material coated with the polymer, the filtersupporting body, and the polymer are measured using an XPS analyzer. Theheight ratio of the peak (286 eV) originating from the —C—O— componentand the peak (289 eV) originating from the —C—O—O— component in the Clsspectrum is determined. The height ratio herein refers to the valuecalculated by dividing the height of the peak originating from the —C—O—component by the height of the peak originating from the —C—O—O—component. In the case of polyethylene terephthalate, since themolecular structure does not have the —C—O— component other than thatoriginating from the —C—O—O— component, the height of the peakoriginating from the —C—O— component is equivalent to the height of thepeak originating from the —C—O—O— component. Therefore, the height ratioof polyethylene terephthalate is 1. Because the above polymer containsthe —C—O— component other than that originating from the —C—O—O—component, the height ratio increases in proportion to the content ofthe polymer. The coating rate can be determined using the followingformula.Coating rate=(A−B)/(C−B)wherein A is the height ratio of the filter material coated with thepolymer, B is the height ratio of the filter supporting body, and C isthe height ratio of the polymer.

To increase contact with blood in a liquid phase, it is desirable forthe filter material for selectively removing leukocytes of the presentinvention to have a configuration with a large surface area. Forexample, fibrous structural materials in the form of a nonwoven fabric,fiber, cotton, yarn, bundle, screen, and fabric; polymer porousmaterials such as sponge; and other structural materials in the form ofbeads, gel, and the like can be given. Fabric and nonwoven fabric areparticularly preferable in view of adsorptivity of leukocytes andhandling easiness as a separating medium. Nonwoven fabric is mostpreferable due to the capability of providing many contact points withleukocytes.

In the case of a fibrous structural material such as nonwoven fabric,the average fiber diameter, which affects the cell adsorptioncapability, is important. If the fiber diameter is too large, the amountand rate of adsorption of leukocytes decrease; if too small, the amountof platelet adsorption increases. The average fiber diameter of thefilter material of the present invention is preferably from 0.5 μm to 50m, and more preferably from 1 μm to 40 μm, and most preferably from 2 μmto 35 μm.

The average fiber diameter in the present invention is determined asfollows. A portion deemed to be substantially homogeneous is sampledfrom one or more pieces of fabrics forming the filter material andphotographed using a scanning electron microscope or the like. Forsampling, an effective filtration cross-sectional area of the fabric isdivided into squares with one side length of 0.5 cm and six squares arerandomly sampled. In random sampling, each divided square is numberedand the required number of squares is selected by using a table ofrandom numbers, for example. Photographs with a magnification of 2,500are taken at three or more, preferably five or more locations for eachsampled square. Photographs for the central parts and the neighborhoodareas of each sampled square are taken until the total number of fiberstaken in the photographs becomes 100. The diameter herein refers to thewidth of fiber in the direction perpendicular to the fiber axis. Then,the average diameter is determined by dividing the sum of the diametersof all measured fibers by the number of the fibers. However, the dataobtained are excluded, for example, in the cases where multiple fibersoverlap precluding diameter measurement of a fiber which hides itselfbehind another fiber, multiple fibers are consolidated into a fiber witha larger diameter due to fusing or else, or there are fibers withremarkably different diameters.

The present invention also provides a filter apparatus for selectiveremoval of leukocytes characterized by having the filter material of thepresent invention filled in a container having at least an inlet portand an outlet port. There are no specific limitations to the shape ofthe container inasmuch as the container has an inlet port and an outletport. Examples of such a container include a container in which thefilter material for selectively removing leukocytes can be filled in theform of laminated layers, a cylindrical container, a columnar containersuch as a triangular prism, a quadratic prism, a hexagonal cylinder, andoctagonal cylinder, a container in which the filter material forselectively removing leukocytes rolled in the form of a cylinder can befilled, and a cylindrical container allowing a blood flow to come intothe cylinder from the outer perimeter, converging blood into theinnermost area, and letting the blood to flow out from an outlet port.Furthermore, a container in which the cross-sectional area decreasesfrom the inlet port toward the outlet port is preferably used.

The filling density of the filter material for selectively removingleukocytes in the container of the present invention, which refers tothe weight of the packed filter material per unit volume of thecontainer, is from 0.05 g/cm³ to 0.5 g/cm³. To increase the efficiencyof selective removal of leukocytes, while ensuring a smooth flow ofblood by preventing clogging of the filter and suppressing a pressureloss increase, the filling density is preferably from 0.075 g/cm³ to 0.4g/cm³, and most preferably from 0.1 g/cm³ to 0.35 g/cm³.

An embodiment of the filter apparatus for selectively removingleukocytes of the present invention will now be specifically describedbelow using the drawings. FIG. 1 is a cross-sectional view of oneembodiment of the filter apparatus for selectively removing leukocytesof the present invention.

In a preferred embodiment of the filter apparatus (1) for selectivelyremoving leukocytes of the present invention, the filter material forselectively removing leukocytes is rolled in the form of a cylinder toprovide a hollow cylindrical filter (4), which is packed in acylindrical container (2) with the both ends (5, 5) being sealedliquid-tight so as not to allow blood to flow. A sealing material withexcellent compatibility with blood when caused to come in contact withblood and possessing liquid-tight properties is used. Known syntheticresins such as urethane can be used. A blood inlet port (3) may beprovided at any optional location of the container which allows theblood to be processed to be supplied to the outer or inner perimeter ofthe hollow cylindrical filter of which the both ends are sealed. A bloodoutlet port (6) may be provided in any location communicated with theinner perimeter when the blood to be processed is supplied to the outerperimeter or any location communicated with the outer perimeter when theblood to be processed is supplied to the inner perimeter.

The hollow cylindrical filter in the filter apparatus for selectiveremoval of leukocytes of the present invention preferably has afiltration area of the first blood contact layer (4 a) from 50 cm² to1,000 cm². The first blood contact layer in the present invention refersto a part of the hollow cylindrical filter with which the blood to beprocessed supplied from the inlet port comes into contact for the firsttime. The first blood contact layer may be any part of the outer orinner perimeter of the hollow cylindrical filter. Platelets are said toabundantly bond with the von Willebrand factor through GPIIb/IIIaacceptor under a high shearing stress and to undergo activated clotting.Therefore, to increase the platelet recovery rate, it is desirable tocause the blood to come into contact with the first contact layermoderately at a low flow rate. If the filtration area of the first bloodcontact layer is less than 50 cm², the blood flow rate per unitfiltration area increases, resulting in a reduction in the plateletrecovery rate. If the filtration area of the first blood contact layeris more than 1,000 cm², a large container is required for the filterapparatus. The filtration area is more preferably from 80 cm² to 500cm², and still more preferably from 100 cm² to 400 cm².

To specify the volume standard specific surface area of the first bloodcontact layer in an appropriate range is preferable from the viewpointof preventing the shearing stress given to platelets. The volumestandard specific surface area as used in the present invention refersto the surface area per unit volume of the filter material and can bemeasured by a known method such as the BET method or the Langmuirmethod. When the filter material is fiber, the volume standard specificsurface area can be calculated using the average fiber diameter, thespecific gravity of fiber, and the like. The hollow cylindrical filterin the filter apparatus for removing leukocytes of the present inventionpreferably has a volume standard specific surface area of the firstblood contact layer in a range from 0.08 m²/ml to 1.0 m²/ml. The volumestandard specific surface area is more preferably from 0.1 m²/ml to 0.8m²/ml, and still more from 0.2 m²/ml to 0.5 m²/ml.

The hollow cylindrical filter in the filter apparatus for removingleukocytes of the present invention may be a scroll of a laminated bodymade of a filter material and a spacer layer material both in the formof a sheet. The term “spacer layer” in the present invention refers to alayer of a material in which blood can flow more easily than in thefilter material for selectively removing leukocytes. A coarse mesh ofmetal, synthetic resin, inorganic fiber, or synthetic fiber, nonwovenfabric with an average fiber diameter larger than the nonwoven fabricused for the hollow cylindrical filter, and the like can be used as thespacer layer material. The spacer layer is laminated with the filtermaterial for selectively removing leukocytes and rolled in the form of ascroll of cloth to secure the area that permits blood to easily flowbetween the hollow cylindrical filter. Both the starting and terminalends of the spacer layer rolled in the form of a scroll are preferablyopen to the outer perimeter and/or the inner perimeter of the hollowcylindrical filter to provide a passage for blood.

The thickness of the hollow cylindrical filter in the leukocyte removalfilter apparatus of the present invention is preferably from 0.6 mm to12.0 mm. If the thickness is less than 0.6 mm, the filtration length istoo small to provide blood components with sufficient opportunity tocontact with the filter material, resulting in a poor leukocyte removalefficiency. If the thickness is more than 12.0 mm, the filtration lengthis so large that blood components are provided with too manyopportunities to contact with the filter material, resulting in adecrease in the platelet recovery rate. A more preferable thicknessrange of the hollow cylindrical filter is from 1.0 mm to 10.0 mm, with astill more preferable thickness range being from 1.5 mm to 8.0 mm.

The hollow cylindrical filter in the filter apparatus for removingleukocytes of the present invention may be provided with a second bloodcontact layer on the downstream side of the first blood contact layer.Since the second blood contact layer has a function of removingleukocytes which have not been removed in the first blood contact layer,the second blood contact layer must have a volume standard specificsurface area larger than that of the first blood contact layer. Apreferable range of the volume standard specific surface area of thesecond blood contact layer is from 1.0 m²/ml to 20 m²/ml, and still morefrom 2.0 m²/ml to 15 m²/ml.

In addition, the thickness ratio of the laminated layers, that is, ofthe second blood contact layer to the first blood contact layer, ispreferably from 0.2 to 10.0. The thickness ratio of the laminated layersin the present invention refers to the value obtained by dividing thethickness of the first blood contact layer by the thickness of thesecond blood contact layer. If the thickness ratio of the laminatedlayers is less than 0.2, the filtration length of the first bloodcontact layer is comparatively small. Therefore, the first blood contactlayer cannot sufficiently mitigate the shearing stress which plateletsreceive in the second blood contact layer, giving rise to a decrease inthe platelet recovery rate. The laminated layer thickness of more than10.0 mm is undesirable because the volume of the first blood contactlayer becomes large, so that a large container is required for thefilter apparatus. For these reasons, the laminated layer thickness ismore preferably from 0.3 to 8.0, and most preferably from 0.5 to 6.0.

The selective leukocyte removal filter apparatus of the presentinvention can be sterilized by a known method such as radiationsterilization, moist heat sterilization, chemical sterilization, gassterilization, and dry heat sterilization. Moist sterilization bymaintaining the filter material under the condition of the saturatedmoisture content or more using a filling liquid is preferable due to thesimple priming operation. A more preferable method is radiationsterilization comprising irradiating the filter material with radiationsuch as γ-ray and electron beams or moist heat sterilization using highpressure steam or the like. Although any liquid not causingdeterioration of the polymer can be used as the filling liquid, water oran aqueous solution of a water soluble substance having a minimal riskof damage to living bodies is preferable.

As the water-soluble substance having a minimal risk of damage to livingbodies, compounds soluble in water exhibiting only a slight damage toliving bodies, for example, salts such as sodium chloride, sodiumcarbonate, sodium hydrogencarbonate, sodium phosphate, sodiumhydrogenphosphate, and sodium pyrosulfite, and water-soluble organiccompounds such as glycerol, sodium citrate, gelatin, and casein can begiven. A compound which may be harmful to living bodies if present in alarge amount can also be used, if such a compound can be washed out fromthe blood cell separating filter by a simple washing procedure such as apriming operation to an extent that only a small amount not harmful tothe living body remains after washing. A compound which can easily forman isotonic solution when dissolved in water may be very preferablyused. These compounds can be used either individually or in combinationof two or more. Preferable water-soluble compounds are sodium chloride,sodium carbonate, sodium hydrogencarbonate, sodium phosphate, sodiumhydrogenphosphate, and sodium pyrosulfite, with sodium chloride beingmost preferable.

The condition of the saturated moisture content or more used herein mayinclude a condition in which the filter material is entirely immersed inwater of an aqueous solution of water soluble compound having a minimalrisk to living bodies or a condition in which the filter material issufficiently humidified in advance to become moistened to the saturatedmoisture content or more of the material. In short, it is sufficient forthe filter material to be exposed to moisture in the amount equivalentto or more of the saturated moisture content of the filter materialirrespective of the degree of exposure.

The concentration of the aqueous solution is preferably 5.0 wt % orless. If the concentration exceeds 5.0 wt %, it is difficult to removethe water-soluble substance by the priming operation. Since elution ofthe polymer can be prevented at a higher more certainty at aconcentration of 0.01 wt % or more, a more preferable concentrationrange is from 0.01 wt % to 4.0 wt %, with a still more preferableconcentration being from 0.1 wt % to 3.0 wt %.

The present invention also provides a system for selective removal ofleukocytes comprising a blood delivery means, an anticoagulant fluidinjection means, and a selective leukocyte removal means which containsthe selective leukocyte removal filter apparatus of the presentinvention. The system for selective removal of leukocytes of the presentinvention can maintain stable selective leukocyte removal capabilitywhile preventing platelet adsorption even if a large amount of blood(e.g. 1-10 l) is processed.

Any known liquid delivery means such as a pump can be used as the blooddelivery means. As the type of the pump, an inner-tube roller pump, afinger pump, and the like can be given. A pump that can accuratelydeliver the blood in a flow rate range from 5 ml/min to 500 ml/min isparticularly preferable in the present invention.

The blood flow rate using the blood delivery means in the selectiveleukocyte removal system of the present invention is preferably from 10ml/min to 200 ml/min. If the blood flow rate is less than 10 ml/min, theblood tends to stagnate in the selective leukocyte removal filterapparatus. If the flow rate is greater than 200 ml/min, the shearingstress significantly increases, resulting in a decrease of the plateletrecovery rate. For these reasons, the blood flow rate is more preferablyfrom 15 ml/min to 150 ml/min, and most preferably from 20 ml/min to 100ml/min.

The anticoagulant fluid injection means used in the present inventionpreferably has a capacity of feeding the anticoagulant fluid to theblood flow circuit at a flow rate from 1% to 20% of the blood flow rate.The anticoagulant may be charged either as is or after dilution. If theflow rate is less than 1% of the blood flow rate, it is difficult forthe anticoagulant to mix with the blood and, therefore, to exhibit asufficient anticoagulation effect. The flow rate of the anticoagulantmore than 20% of the blood flow rate is not desirable in practice,because the blood may be excessively diluted. For these reasons, theflow rate of the anticoagulant fluid is more preferably from 3% to 18%,and most preferably from 5% to 18% of the blood flow rate.

As the type of the anticoagulant contained in the anticoagulant fluidused in the present invention, heparins such as heparin sodium, heparincalcium, and dalteparin sodium; protease inhibitors such as nafamostatmesilate and gabexate mesilate; and citric acid-based anticoagulantssuch as ACD-A, ACD-B, and CPD; and the like can be preferably used. Theabove anticoagulants can be used more efficiently, when diluted with abuffer solution such as a physiological saline solution or a glucosesolution which neither affects the anticoagulation effect nor denaturesblood constituents.

In the case of heparin or a low molecular weight heparin, for example,the amount of the anticoagulant added to 1 l of blood is from 100 to2,000 units, and preferably from 300 to 1,500 units. In the case ofnafamostat mesilate, the amount is from 2 to 40 mg, and preferably from6 to 30 mg. In the case of ACD-A or ACD-B solution, the effectiveanticoagulant amount is from 20 to 160 ml, and preferably from 30 to 125ml.

As the means for adding an anticoagulant solution, any means typified bycommonly used metering pumps such as a roller inner tube pump, fingerpump, infusion pump, and syringe pump can be used. More specifically, aninner tube roller pump, a finger pump, and the like by which a verysmall quantity of a fluid can be injected at a high precision can besuitably used.

The selective leukocyte removal system of the present invention can beconstructed by liquid-tight joining of the above-described blooddelivery means, anticoagulant fluid injection means, and selectiveleukocyte removal means using a blood circuit to introduce blood to theselective leukocyte removal means and a blood circuit to discharge theblood from the selective leukocyte removal means, thereby forming acircuit for extracorporeal circulation. To form the entireconfiguration, the blood delivery means and the anticoagulant fluidinjection means are provided in the circuit on the blood introductionside having a blood recovering means, for example, and this circuit isjoined to the blood inlet port side of the selective leukocyte removalmeans. The system can be preferably used for extracorporeal circulationif the blood discharge side circuit having a means for returning bloodto the patient is provided on the blood exit side of the selectiveleukocyte removal means.

FIG. 2 is a schematic diagram showing one embodiment of the selectiveleukocyte removal system of the present invention. In the selectiveleukocyte removal system of FIG. 1, the system comprises a means (7) toextract blood from a patient, an anticoagulant fluid injection means (8)to inject an anticoagulant fluid (8 a) into the extracted blood, a blooddelivery means (9) to deliver the blood mixed with the anticoagulant ata flow rate of 10-200 ml/min, a micro aggregate capture means (12)having an arterial pressure monitor (12 a) and a selective leukocyteremoval filter apparatus. A selective leukocyte removal means (10)having an inlet port and a blood outlet port, a drip chamber (13) havinga venous pressure monitor (13 a), and a means (11) to return the bloodto the patient are liquid tightly connected in that order.

The present invention also provides a method of using the selectiveleukocyte removal filter material for treating cellular immuneabnormality, comprising causing the blood of a patient suffering fromthe cellular immune abnormality to come in contact with the filter ofthe present invention. To complete the medical treatment of the diseaseusing the method of the present invention, the blood after processingmay be returned to the patient. This can be preferably carried out byapplying various means and methods of use described in connection withthe selective leukocyte removal system. The cellular immune abnormalityas used in the present invention refers to a disease in whichimmunocompetent cells, cytotoxic-T cells, inflammatory cells, and thelike in the living body present abnormalities to produce an inflammationinducing substance such as cytokine, by which the body tissues areattacked. Autoimmune diseases such as or malignant rheumatoid arthritis,systemic erythematodes, Behcet's disease, idiopathic thrombo cytopenicpurpura, and autoimmune hepatitis; inflammatory bowel diseases such asulcerative colitis and Crohn's disease; allergic diseases such as atopicdermatitis; rapidly progressive glomerulonephritis; and systemicinflammatory response syndrome are given as examples.

It is desirable that the selective leukocyte removal system of thepresent invention has leukocyte removal capability in terms of theleukocyte removal rate of 50% or more. The leukocyte removal rate can bedetermined in the present invention from the leukocyte concentration inthe blood on the inlet port side introduced into the selective leukocyteremoval means and the leukocyte concentration in the blood on the outletport side discharged from the selective leukocyte removal meansaccording to the following formula.Leukocyte removal rate (%)=(1−Leukocyte concentration on the outlet portside/Leukocyte concentration on the inlet port side)×100

If the leukocyte removal rate is less than 50%, the amount of leukocytesremoved in one process is not sufficient, only giving a limitedimprovement effect on the cellular immune abnormality. A more preferableleukocyte removal rate is 60% or more, with a 70% or more leukocyteremoval rate being most preferable.

In regard to the platelet recovery capability, it is desirable that theplatelet recovery rate is 50% or more. The platelet recovery rate can bedetermined in the present invention from the platelet concentration inthe blood on the inlet port side introduced into the selective leukocyteremoval means and the platelet concentration in the blood on the outletport side discharged from the selective leukocyte removal meansaccording to the following formula.Platelet recovery rate (%)=(Platelet concentration on the outlet portside/Platelet concentration on the inlet port side)×100

If the platelet recovery rate is less than 50%, the amount of plateletrecovered may be too small when processing blood containing a smallamount of platelets (e.g. 100,000 platelets/μl or less). A morepreferable platelet recovery rate is 60% or more, with a 70% or moreplatelet recovery rate being most preferable.

EXAMPLES

The present invention is described below by examples, which should notbe construed as limiting the present invention.

Example 1

(Synthesis of Polymer)

One example of the method of synthesizing the polymer used for preparinga selective leukocyte removal filter by coating will be shown. Areaction vessel equipped with a reflux condenser was charged withethanol (277 ml). After bubbling nitrogen into ethanol and stirring themixture at 73° C. for one hour, monomers were added dropwise over 120minutes while maintaining a nitrogen atmosphere. An initiator solutionwas added dropwise at the same time over 300 minutes. After completionof the addition of the initiator solution, the monomers were polymerizedfor further two hours.

The monomer mixture was a liquid containing 4.8 g (30.0 mmol) ofmethoxydiethylene glycol methacrylate (MDG), which is a polymerizablemonomer having an alkylene oxide chain, 4.3 g (50.0 mmol) ofmethylmethacrylate (MMA), which is a polymerizable monomer having ahydrophobic group, and 2.7 g (20.0 mmol) of 2-hydroxyisobutylmethacrylate (HBMA), which is a polymerizable monomer having a hydroxylgroup. The molar ratio of the monomers was 30 mol % (MDG): 50 mol %(MMA): 20 mol % (HBMA). An ethanol solution containing 0.034 g ofazobisdimethylvaleronitrile (V-65) was used as the initiator solution.The reaction mixture was added dropwise to purified water to cause thepolymer to precipitate. The recovered polymer precipitate was cut intopieces and once again put into purified water, followed by stirring forone hour to wash the polymer. Next, the washed polymer was dried undervacuum at 60° C. to obtain the target polymer.

The composition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 10.29. The weight average molecular weight of thepolymer measured by GPC was 6.8×10⁵.

(Preparation of Filter Material)

Next, a method of preparing the filter material for selectively removingleukocytes will be described. 1 g of the polymer obtained was dissolvedin 100 ml of a mixed solvent of ethanol and purified water (70:30). Anonwoven fabric made from polyethylene terephthalate was immersed in thesolvent. After removing excessive liquid, the nonwoven fabric was driedat room temperature for 16 hours to obtain the target filter. The δvalue of the filter supporting body was 10.30, the average fiberdiameter of the filter material was 2.7 μm, the density was 90 g/m², andthe thickness was 0.42 mm.

(Elution Test)

The method of the elution test was as follows. A 200 ml container waspacked with 15 g of the filter material prepared in the above, aphysiological saline solution was filled into the container, and thecontent was sterilized with γ-ray (irradiation dose: 25 kGy). To confirmelution in the temperature range possibly occurring during actualpreservation of medical devices, the container was allowed to stand at25° C. for 24 hours, then at 4° C. for 24 hours. The appearance of thefilled solution after preservation was observed to confirm that thesolution was transparent and colorless, with no change as compared withthe state before sterilization. The maximum absorbance of the filledsolution was measured using an ultraviolet spectrophotometer (V-560,manufactured by JASCO Corp.) at a wavelength of 220 nm to 350 nm to findthat the maximum absorbance was 0.04.

(Evaluation of Blood Properties)

Next, a test method for evaluating the leukocyte removal rate andplatelet recovery rate will be described. The filter material preparedin the above was cut into disks, each with a diameter of 6.8 mm. Sevensheets of the disks were laminated in a 1 ml column having an inlet portand an outlet port. The column was filled with a physiological salinesolution and sterilized with γ-ray (irradiation dose: 25 kGy) to preparethe column for performance evaluation. 3 ml of fresh human blood (numberof leukocytes: 4,500-8,400/μl, number of platelets: 150,000-440,000/μl)to which ACD-A was added as an anti-coagulator (blood:ACD-A=8:1) was fedinto the column from the inlet port using a syringe pump at a constantflow rate of 0.5 ml/min. The processed blood was recovered. Theleukocyte concentration and platelet concentration in the blood beforeand after passing through the column were measured using an automaticblood cell counter (Sysmex SF-3000, manufactured by To a MedicalElectronics Co., Ltd.), and the leukocyte removal rate and the plateletrecovery rate were calculated.

As a result, the leukocyte removal rate was 97.5% and the plateletrecovery rate was 85.0%, confirming selective leukocyte removalcapability.

Example 2

A polymer was synthesized in the same manner as in Example 1, except forusing 40.0 mol % of MDG, 50.0 mol % of MMA, and 10 mol % of HBMA. Thecomposition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The γ value of thepolymer was calculated according to the Fedors method to confirm thatthe γ value was 10.04. The weight average molecular weight of thepolymer measured by GPC was 8.7×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The appearance of the filled solution after sterilization andpreservation confirmed that the solution was transparent and colorless,with no change as compared with the state before sterilization. Themaximum absorbance of the filled solution was measured using anultraviolet spectrophotometer at a wavelength of 220 nm to 350 nm tofind that the maximum absorbance was 0.05. The leukocyte removal ratewas 97.0% and the platelet recovery rate was 85.0%, confirming selectiveleukocyte removal capability.

Example 3

A polymer was synthesized in the same manner as in Example 1, except forusing 20 mol % of MDG, 60 mol % of MMA, and 20 mol % of HBMA. Thecomposition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 10.31. The weight average molecular weight of thepolymer measured by GPC was 9.2×10⁵.

1 g of the polymer obtained was dissolved in 100 ml of a mixed solventof ethanol and purified water (70:30). A nonwoven fabric made frompolypropylene was immersed in the solvent. After removing excessiveliquid, the nonwoven fabric was dried at room temperature for 16 hoursto obtain the target filter. The δ value of the filter supporting bodywas 7.90, the average fiber diameter of the filter material was 2.6 μm,the density was 80 g/m², and the thickness was 0.51 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The appearance of the filled solution after sterilization andpreservation confirmed that the solution was transparent and colorless,with no change as compared with the state before sterilization. Themaximum absorbance of the filled solution was measured using anultraviolet spectrophotometer at a wavelength of 220 nm to 350 nm tofind that the maximum absorbance was 0.08. The leukocyte removal ratewas 98.5% and the platelet recovery rate 89.4%, confirming selectiveleukocyte removal capability.

Example 4

A polymer was synthesized in the same manner as in Example 1, except forusing n-butyl methacrylate (BMA) as a polymerizable monomer having ahydrophobic group and 2-hydroxyisopropyl methacrylate (HPMA) as apolymerizable monomer having a hydroxyl group, and charging 20 mol % ofMDG, 50 mol % of BMA, and 30 mol % of HPMA. The composition of theresulting polymer was analyzed from the integral value of NMRmeasurement, confirming that the composition was almost in agreementwith the charged monomer composition. The δ value of the polymer wascalculated according to the Fedors method to confirm that the δ valuewas 10.46. The weight average molecular weight of the polymer measuredby GPC was 1.1×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The appearance of the filled solution after sterilization andpreservation confirmed that the solution was transparent and colorless,with no change as compared with the state before sterilization. Themaximum absorbance of the filled solution was measured using anultraviolet spectrophotometer at a wavelength of 220 nm to 350 nm tofind that the maximum absorbance was 0.08. The leukocyte removal ratewas 93.8% and the platelet recovery rate was 83.7%, confirming selectiveleukocyte removal capability.

Example 5

A polymer was synthesized in the same manner as in Example 1, except forusing 15 mol % of MDG, 40 mol % of MMA, and 45 mol % of HBMA. Thecomposition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 10.86. The weight average molecular weight of thepolymer measured by GPC was 2.1×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The appearance of the filled solution after sterilization andpreservation confirmed that the solution was transparent and colorless,with no change as compared with the state before sterilization. Themaximum absorbance of the filled solution was measured using anultraviolet spectrophotometer at a wavelength of 220 nm to 350 nm tofind that the maximum absorbance was 0.15. The leukocyte removal ratewas 82.2% and the platelet recovery rate was 80.2%, confirming selectiveleukocyte removal capability.

Comparative Example 1

A polymer was synthesized in the same manner as in Example 1, except forusing 5.0 mol % of MDG, 5.0 mol % of MMA, and 90.0 mol % of HPMA. Thecomposition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 12.39. The weight average molecular weight of thepolymer measured by GPC was 3.2×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The filled solution after sterilization and preservation was turbid,confirming that the polymer eluted during sterilization andpreservation. The maximum absorbance of the filled solution was measuredusing an ultraviolet spectrophotometer at a wavelength of 220 nm to 350nm to find that the maximum absorbance was 2.4. The leukocyte removalrate was 93.3% and the platelet recovery rate 3.1%, confirming a lowplatelet recovery rate.

Comparative Example 2

A polymer was synthesized in the same manner as in Example 1, except forusing methoxynonaethylene glycol methacrylate (MNG) as a polymerizablemonomer having a polyalkylene oxide chain and charging 65.0 mol % of MNGand 35.0 mol % of MMA. The composition of the resulting polymer wasanalyzed from the integral value of NMR measurement, confirming that thecomposition was almost in agreement with the charged monomercomposition. The δ value of the polymer was calculated according to theFedors method to confirm that the δ value was 9.64. The weight averagemolecular weight of the polymer measured by GPC was 2.2×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The filled solution after sterilization and preservation was turbid,confirming that the polymer eluted during sterilization andpreservation. The maximum absorbance of the filled solution was measuredusing an ultraviolet spectrophotometer at a wavelength of 220 nm to 350nm to find that the maximum absorbance was 5.0 or more. The leukocyteremoval rate was 99.5% and the platelet recovery rate was 52.0%.

Comparative Example 3

A polymer was synthesized in the same manner as in Example 1, except forusing 5.0 mol % of MDG, 50.0 mol % of MMA, and 45.0 mol % of HBMA. Thecomposition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 10.89. The weight average molecular weight of thepolymer measured by GPC was 1.2×10⁵.

1 g of the polymer obtained was dissolved in 100 ml of a mixed solventof ethanol and purified water (70:30). A nonwoven fabric made fromcellulose was immersed in the solvent. After removing excessive liquid,the nonwoven fabric was dried at room temperature for 16 hours to obtainthe target filter. The δ value of the filter supporting body was 15.65,the average fiber diameter of the filter material was 4.1 μm, thedensity was 18 g/m², and the thickness was 0.1 mm.

Using the prepared filter material, the elution test was carried out inthe same manner as in Example 1. The filled solution after sterilizationand preservation was turbid, confirming that the polymer eluted duringsterilization and preservation. The maximum absorbance of the filledsolution was measured using an ultraviolet spectrophotometer at awavelength of 220 nm to 350 nm to find that the maximum absorbance was5.0 or more.

The filter material prepared in the above was cut into disks, each witha diameter of 6.8 mm. 28 sheets of the disks were laminated in a 1 mlcolumn having an inlet port and an outlet port. The blood performancetest was carried out in the same manner as in Example 1. The leukocyteremoval rate was 85.1% and the platelet recovery rate 45.4%, confirmingrather low recovery rate of platelets.

Comparative Example 4

A polymer was synthesized in the same manner as in Example 1, except forusing 90.0 mol % of MDG and 10.0 mol % of MMA. The composition of theresulting polymer was analyzed from the integral value of NMRmeasurement, confirming that the composition was almost in agreementwith the charged monomer composition. The δ value of the polymer wascalculated according to the Fedors method to confirm that the δ valuewas 9.70. The weight average molecular weight of the polymer measured byGPC was 3.5×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The filled solution after sterilization and preservation was turbid,confirming that the polymer eluted during sterilization andpreservation. The maximum absorbance of the filled solution was measuredusing an ultraviolet spectrophotometer at a wavelength of 220 nm to 350nm to find that the maximum absorbance was 5.0 or more. The leukocyteremoval rate was 97.0% and the platelet recovery rate was 78.0%.

Comparative Example 5

A polymer was synthesized in the same manner as in Example 1, except forusing 40.0 mol % of MDG, 25.0 mol % of MMA, and 35.0 mol % of HBMA. Thecomposition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 10.58. The weight average molecular weight of thepolymer measured by GPC was 4.2×10⁵.

A filter material was prepared from the polymer in the same manner as inExample 1. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.7 μm, the densitywas 90 g/m², and the thickness was 0.42 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The filled solution after sterilization and preservation was turbid,confirming that the polymer eluted during sterilization andpreservation. The maximum absorbance of the filled solution was measuredusing an ultraviolet spectrophotometer at a wavelength of 220 nm to 350nm to find that the maximum absorbance was 2.3. The leukocyte removalrate was 85.8% and the platelet recovery rate was 72.7%.

Example 6

Polymerization was carried out at 70° C. for six hours using 2.3 g (12mmol) of MDG monomer, 2.0 g (20 mmol) of MMA monomer, and 1.3 g (8 mmol)of HBMA monomer (MDG:MMA:HBMA=30:50:20, in molar ratio), 300 ml ofethanol, and 0.1 g of V-65. The obtained reaction mixture was addeddropwise to 10 l of water while stirring to cause the polymer toprecipitate and the polymer was recovered as water-insoluble substance.The composition of the resulting polymer was analyzed from the integralvalue of NMR measurement, confirming that the composition was almost inagreement with the charged monomer composition. The δ value of thepolymer was calculated according to the Fedors method to confirm thatthe δ value was 10.29. The weight average molecular weight of thepolymer measured by GPC was 4.0×10⁴.

1 g of the polymer thus obtained was dissolved in 99 g of a 70% aqueoussolution of ethanol to obtain a 1% coating solution. 1 g of a nonwovenfabric made from polyethylene terephthalate was immersed in 10 ml of the1% coating solution and dried at 25° C. for 12 hours to obtain a filtermaterial. The δ value of the filter supporting body was 10.30, theaverage fiber diameter of the filter material was 2.9 μm, the densitywas 90 g/m², and the thickness was 0.40 mm.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The appearance of the filled solution after sterilization andpreservation was transparent and colorless. The maximum absorbance ofthe filled solution measured using an ultraviolet spectrophotometer at awavelength of 220 nm to 350 nm was 0.41, indicating elution of a smallamount of the polymer. The leukocyte removal rate was 95.1% and theplatelet recovery rate was 74.3%.

The results are summarized in Table 1. TABLE 1 Example ComparativeExample 1 2 3 4 5 6 1 2 3 4 5 Polymerizable monomer having 30 40 20 2015 30 5 65 5 90 40 polyalkylene oxide chain (mol %) Polymerizablemonomer having 50 50 60 50 40 50 5 35 50 10 25 a hydrophobic group (mol%) Polymerizable monomer having 20 10 20 30 45 20 90 0 45 0 35 hydroxylgroup (mol %) Weight average molecular 6.8 × 8.7 × 9.2 × 1.1 × 7.2 × 4.0× 3.2 × 2.2 × 1.2 × 3.5 × 4.2 × weight of polymer 10⁵ 10⁵ 10⁵ 10⁵ 10⁵10⁴ 10⁵ 10⁵ 10⁵ 10⁵ 10⁵ δ-Value of polymer 10.29 10.04 10.31 10.46 10.8610.29 12.39 9.64 10.89 9.70 10.58 δ-Value of filter 10.30 10.30 7.9010.30 10.30 10.30 10.30 10.30 15.65 10.30 10.30 supporting body Elutiontest: Filling solution appearance * Tp Tp Tp Tp Tp Tp Cl Cl Cl Cl ClUV_(max(220-350 nm)) 0.04 0.05 0.08 0.08 0.15 0.412.4 >5.0 >5.0 >5.0 >2.3 Blood performance test: Leukocyte removal rate(%) 97.5 97.0 98.5 93.8 82.2 95.1 93.3 99.5 85.1 97.0 85.8 Plateletrecovery rate (%) 85.0 85.0 89.4 83.7 80.2 74.3 3.1 52.0 45.4 78.0 72.7* Tp: Transparent, Cl: Cloudy

As can be seen from Table 1, the filter materials using a polymercomprising a unit originating from a polymerizable monomer having apolyalkylene oxide chain, a unit originating from a polymerizablemonomer having a hydrophobic group, and a unit originating from apolymerizable monomer having a hydroxyl group at a specific ratio wereconfirmed to elute only a minimal amount of polymer components and toexhibit selective leukocyte removal capability. On the other hand, thefilter materials using a polymer not satisfying these conditions did notsatisfy either the elution test or the blood performance test, or both.Furthermore, the filter material using a polymer with a weight averagemolecular weight of 100,000 or more was found to achieve excellentresults in the eluting test.

Example 7

The filter material was prepared in the same manner as in Example 1,except that 10 g of the polymer was dissolved in 100 ml of a mixedsolvent of ethanol and purified water (70:30). The polymer retained bythe filter material was measured to find that the filter materialcontained was 20 wt % of the polymer as compared with 2 wt % in thefilter material of Example 1. The amount of the polymer retained by thefilter material was calculated from the weight change of the filtermaterial before and after coating.

Using the obtained filter material, the elution test and the bloodperformance test were carried out in the same manner as in Example 1.The appearance of the filled solution after sterilization andpreservation was transparent and colorless. The maximum absorbance ofthe filled solution was measured using an ultraviolet spectrophotometerat a wavelength of 220 nm to 350 nm to find that the maximum absorbancewas 0.21. As a result, the leukocyte removal rate was 92.3% and theplatelet recovery rate 82.1%, confirming the selective leukocyte removalcapability.

Example 8

(Preparation of Selective Leukocyte Removal Filter Apparatus)

Next, a method of preparing the selective leukocyte removal filterapparatus used in the method for selectively removing leukocytes will bedescribed. 4.0 g of the polymer obtained in Example 1 was dissolved in500 ml of a mixed solvent of ethanol and purified water (70:30). Anonwoven fabric made from polyethylene terephthalate with an averagefiber diameter of 2.7 μm, a density of 90 g/m², and a thickness of 0.42mm was immersed in the solvent. After removing excessive liquid, thenonwoven fabric was dried at room temperature for 16 hours to obtain afilter material (A). 0.5 g of the polymer obtained in Example 1 wasdissolved in 500 ml of a mixed solvent of ethanol and purified water(70:30). A nonwoven fabric made from polyethylene terephthalate with anaverage fiber diameter of 12 μm, a density of 30 g/m², and a thicknessof 0.20 mm was immersed in the solvent. After removing excessive liquid,the nonwoven fabric was dried at room temperature for 16 hours to obtaina filter material (B).

The filter material (A) was cut into a sheet (width: 150 m, length: 250mm) and the sheet was wound around a cylindrical polyethylene mesh witha diameter of 28 mm. The filter material (B) cut into a rectangle of 150mm×1,660 mm was wound around the cylinder and laminated over the filtermaterial (A). A polyethylene mesh with a width of 150 mm and a length of130 mm was further wound around the filter material (B) to obtain ahollow cylindrical filter. After sealing both ends by polyurethane, thecylinder was placed in a cylindrical polycarbonate container with aninternal diameter of 41 mm of which the top and the bottom wererespectively provided with a blood inlet port and a blood outlet port,so that the outer circumference of the cylinder was connected to theblood inlet port of the container and the inner circumference of thecylinder was connected to the blood outlet port of the container. Thecontainer was filled with a physiological saline solution and sterilizedwith δ-ray (irradiation dose: 25 kGy) to prepare a selective leukocyteremoval filter apparatus. In the selective leukocyte removal filterapparatus, the filling density of the filter material was 0.157 g/cm³,the filtration area of the first blood contact layer was 174 cm², thevolume standard specific surface area of the first blood contact layerwas 0.33 m²/ml, the volume standard specific surface area of the secondblood contact layer was 1.5 m²/ml, the laminated layer thickness ratioof the first blood contact layer to the second blood contact layer was4.0, and the thickness of the hollow cylindrical filter was 4.5 mm.

(Method of Extracorporeal Circulation Using Selective Leukocyte RemovalSystem)

A selective leukocyte removal system for treating blood of a patient ofulcerative colitis shown in FIG. 2 was prepared. Extracorporealcirculation, each treatment being for one hour at a flow rate of 50ml/min, was conducted five times for each patient at a frequency of oncea week using the selective leukocyte removal system in which the abovefilter apparatus was used. As an anticoagulant solution, a mixture of3,000 units of heparin and 500 ml of a physiological saline solution wascontinuously injected at a flow rate of 8 ml/min.

At 30 minutes after initiation of extracorporeal circulation, bloodsamples were recovered at locations before and after the selectiveleukocyte removal means to determine the leukocyte concentration andplatelet concentration using an automatic blood cell counter. Theleukocyte removal rate and the platelet recovery rate were calculatedfrom the found concentrations. As a result, the leukocyte removal ratewas 82% and the platelet recovery rate was 65%. A high platelet recoveryrate was attained. After 5 treatments, the number of diarrheaoccurrences of the patient decreased from 11 times/day to 4 times/day,confirming improvement of the symptom.

Example 9

A selective leukocyte removal system for treating blood of a patient ofrheumatism shown in FIG. 2 was prepared. Extracorporeal circulation,each treatment being for one hour at a flow rate of 50 ml/min, wasconducted seven times for each patient at a frequency of once a weekusing the selective leukocyte removal system in which the filterapparatus of Example 8 was used. As an anticoagulant solution, a mixtureof 250 ml of ACD-A solution and 250 ml of a physiological salinesolution was continuously injected at a flow rate of 8 ml/min.

At 30 minutes after initiation of extracorporeal circulation, bloodsamples were recovered at locations before and after the selectiveleukocyte removal means to determine the leukocyte concentration andplatelet concentration using an automatic blood cell counter. Theleukocyte removal rate and the platelet recovery rate were calculatedfrom the found concentrations. As a result, the leukocyte removal ratewas 75% and the platelet recovery rate was 82%. A high platelet recoveryrate was attained. The Ritchie index (see Ritchie Index, Index toevaluate the conditions of articular rheumatism patient, Ritchie et al.Quarterly Journal of Medicine, New Series XXXVII, No. 147, p. 393-406,July 1968) of the patient after 7 treatments decreased from 15 points to8 points, showing improvement in the symptom.

Example 10

The filter material (B) of Example 8 was cut into a sheet (width: 150mm, length: 1,500 mm) and the sheet was wound around a cylindrical meshwith a diameter of 31 mm made from polyethylene. A polyethylene meshwith a width of 150 mm and a length of 130 mm was further wound aroundthe filter material (B) to obtain a hollow cylindrical filter. Aselective leukocyte removal filter apparatus was prepared in the samemanner as in Example 8. In the selective leukocyte removal filterapparatus, the filling density of the filter material was 0.145 g/cm³,the filtration area of the first blood contact layer was 174 cm², thevolume standard specific surface area of the first blood contact layerwas 0.33 m²/ml, and the thickness of the hollow cylindrical filter was3.0 mm.

A selective leukocyte removal system for treating blood of a patient ofsystemic inflammatory response syndrome shown in FIG. 2 was prepared.Extracorporeal circulation for one hour at a flow rate of 50 ml/min wasconducted for the patient using the selective leukocyte removal systemin which the above filter apparatus was used. As an anticoagulantsolution, a mixture of 3,000 units of heparin and 500 ml of aphysiological saline solution was continuously injected at a flow rateof 8 ml/min.

At 30 minutes after initiation of extracorporeal circulation, bloodsamples were recovered at locations before and after the selectiveleukocyte removal means to determine the leukocyte concentration andplatelet concentration using an automatic blood cell counter. Theleukocyte removal rate and the platelet recovery rate were calculatedfrom the found concentrations. As a result, the leukocyte removal ratewas 58% and the platelet recovery rate was 92%. A high platelet recoveryrate was attained. Moreover, TNF-α production capability originatingfrom culture supernatant of the mononuclear cell in the patient'speripheral blood before and after the treatment was determined. Fordetermining the TNF-α production capability, a mononuclear cell layerwas separated from the blood using a Conray-Ficoll solution, the cellswere stimulated with Concanavarin A (Con A) at a final concentration of7 mg/ml per 1×10⁶ mononuclear cells, then the cells were cultured for 24hours to measure the TNF-α concentration of the supernatant. As aresult, the concentration of 9,100 pg/ml before the treatment decreasedto 4,800 pg/ml after the treatment, confirming suppression of thedisease. Since TNF-α activates leukocytes (neutrophil leucocytes) andinduces a tissue damage, the decrease in the concentration is supposedto improve the inflammation symptom.

INDUSTRIAL APPLICABILITY

As is clear from the above description, the present invention provides apolymer excelling in biocompatibility, exhibiting, in particular, only alow adsorption to platelets, and having a low elution property. Thefilter material for selectively removing leukocytes, the selectiveleukocyte removal filter apparatus, and the selective leukocyte removalsystem using the biocompatible polymer can selectively remove leukocytesfrom various bloods, particularly from whole blood, while inhibitingadsorption of platelets, and are useful for platelet transfusion andextracorporeal circulation for leukocyte removal.

1-40. (canceled)
 41. A selective leukocyte removal filter materialwherein a biocompatible polymer comprising 8-45 mol % of a unitoriginating from a polymerizable monomer having a polyalkylene oxidechain, 30-90 mol % of a unit originating from a polymerizable monomerhaving a hydrophobic group, and 2-50 mol % of a unit originating from apolymerizable monomer having a hydroxyl group is present on at least thesurface of a filter supporting body.
 42. A selective leukocyte removalfilter material according to claim 41, wherein the polymer has a weightaverage molecular weight of 100,000 to 3,000,000.
 43. A selectiveleukocyte removal filter material according to claim 41, wherein thecontent ratio of the unit originating from the polymerizable monomerhaving a hydroxyl group to the unit originating from the polymerizablemonomer having a hydrophobic group is from 0.05 to
 1. 44. A selectiveleukocyte removal filter material according to claim 41, wherein thepolymer is a nonionic polymer.
 45. A selective leukocyte removal filtermaterial according to claim 41, wherein the polymerizable monomer havinga hydroxyl group has solubility in water at 20° C. in the range from 3wt % or more, but less than 50 wt %.
 46. A selective leukocyte removalfilter material according to claim 45, wherein the polymerizable monomerhaving a hydroxyl group is 2-hydroxyisobutyl (meth)acrylate.
 47. Theselective leukocyte removal filter material according to claim 41,wherein the polymer has a solubility factor (δ value) of 10.0 to 11.5and the filter supporting body has a solubility factor (δ value) of 7.0to 15.0.
 48. The filter material according to claim 41, wherein theamount of the polymer held on the filter supporting body is 0.001 wt %or more, but less than 10 wt %.
 49. The filter material according toclaim 41, wherein the polymer coating rate of the filter supporting bodyis from 40% to 90%.
 50. The filter material according to claim 41,wherein the filter material is a woven fabric or nonwoven fabric. 51.The filter material according to claim 50, wherein the average fiberdiameter of the woven or nonwoven fabric is from 0.5 μm to 50 μm and thefilling density is from 0.05 g/cm³ to 0.5 g/cm³.
 52. The selectiveleukocyte removal filter material according to claim 41, used forselectively removing leukocytes from blood extracted from a patient ofcellular immune abnormality.
 53. The selective leukocyte removal filtermaterial according to claim 52, wherein the disease is chronic ormalignant rheumatoid arthritis, systemic erythematodes, Behcet'sdisease, idiopathic thrombo cytopenic purpura, autoimmune hepatitis,ulcerative colitis, Crohn's disease, atopic dermatitis, rapidlyprogressive glomerulonephritis, or systemic inflammatory responsesyndrome.
 54. A selective leukocyte removal filter apparatus comprisingthe filter material according to claim 41, packed in a container havingat least a blood inlet port and a blood outlet port.
 55. The selectiveleukocyte removal filter apparatus according to claim 54, wherein ahollow cylindrical filter formed from the filter material wound in theshape of a cylinder is packed in the container with both ends sealed,and either the blood inlet port or the blood outlet port is providedcommunicating with either the inner perimeter or the outer perimeter ofthe cylindrical filter material.
 56. The selective leukocyte removalfilter apparatus according to claim 55, wherein the hollow cylindricalfilter has a configuration of a scroll of a laminated body made of a)the filter material in the form of a sheet and b) a spacer layermaterial in the form of a sheet allowing blood to pass through, thestarting and/or terminal ends of the spacer layer rolled in the form ofa scroll being open to the outer perimeter and/or the inner perimeter ofthe hollow cylindrical filter to provide a passage for blood.
 57. Theselective leukocyte removal filter apparatus according to claim 55,wherein the hollow cylindrical filter has a first blood contact layerwith an area from 50 cm² to 1,000 cm².
 58. The selective leukocyteremoval filter apparatus according to claim 57, wherein the volumestandard specific surface area of the first blood contact layer is 0.08m²/ml or more, but less than 1.0 m²/ml.
 59. The selective leukocyteremoval filter apparatus according to claim 58, wherein the hollowcylindrical filter has a second blood contact layer with a volumestandard specific surface area of 1.0 m²/ml or more, but less than 20m²/ml.
 60. The selective leukocyte removal filter apparatus according toclaim 59, wherein the thickness ratio of the second blood contact layerto the first blood contact layer is from 0.2 to 10.0.
 61. The selectiveleukocyte removal filter apparatus according to claim 55, wherein thethickness of the hollow cylindrical filter is from 0.6 mm to 12.0 mm.62. The selective leukocyte removal filter apparatus according to claim54, wherein the filter material is maintained under the condition of thesaturated moisture content or more using water or an aqueous solution ofa water-soluble substance with a minimal risk of damage to living bodiesand is sterilized.
 63. The selective leukocyte removal filter apparatusaccording to claim 62, wherein the concentration of the water-solublesubstance in the aqueous solution is 5 wt % or less.
 64. The selectiveleukocyte removal filter apparatus according to claim 62, wherein thewater-soluble substance is sodium chloride.
 65. The selective leukocyteremoval filter apparatus according to claim 54, used for selectivelyremoving leukocytes from blood extracted from a patient of cellularimmune abnormality.
 66. The selective leukocyte removal filter apparatusaccording to claim 65, wherein the disease is chronic or malignantrheumatoid arthritis, systemic erythematodes, Behcet's disease,idiopathic thrombo cytopenic purpura, autoimmune hepatitis, ulcerativecolitis, Crohn's disease, atopic dermatitis, rapidly progressiveglomerulonephritis, or systemic inflammatory response syndrome.
 67. Aselective leukocyte removal system comprising a blood delivery means, ananticoagulant fluid injection means, and a selective leukocyte removalmeans, wherein the selective leukocyte removal means comprises theselective leukocyte removal filter apparatus according to claim
 54. 68.The selective leukocyte removal system according to claim 67, whereinthe blood delivery means delivers blood in a quantity from 1 l to 10 lat a flow rate of 10 ml/min to 200 ml/min.
 69. The selective leukocyteremoval system according to claim 67, wherein the anticoagulant fluidinjection means injects an anticoagulant fluid at a rate of 1% to 20% ofthe blood flow rate.
 70. The selective leukocyte removal systemaccording to claim 67, wherein the anticoagulant fluid injected from theanticoagulant fluid injection means comprises heparin or a low molecularweight heparin.
 71. The selective leukocyte removal system according toclaim 67, wherein the anticoagulant fluid injected from theanticoagulant fluid injection means comprises a protease inhibitor. 72.The selective leukocyte removal system according to claim 67, whereinthe anticoagulant fluid injected from the anticoagulant fluid injectionmeans comprises an ACD-A solution or an ACD-B solution.
 73. Theselective leukocyte removal system according to claim 70, wherein theamount of anticoagulant fluid injected is from 100 units to 2,000 unitsper 1 l of blood.
 74. The selective leukocyte removal system accordingto claim 71, wherein the amount of anticoagulant fluid injected is from2 mg to 40 mg per 1 l of blood.
 75. The selective leukocyte removalsystem according to claim 72, wherein the amount of anticoagulant fluidinjected is from 20 ml to 160 ml per 1 l of blood.
 76. The selectiveleukocyte removal system according to claim 67, used for selectivelyremoving leukocytes from blood extracted from a patient of cellularimmune abnormality.
 77. The selective leukocyte removal system accordingto claim 76, wherein the disease is chronic or malignant rheumatoidarthritis, systemic erythematodes, Behcet's disease, idiopathic thrombocytopenic purpura, autoimmune hepatitis, ulcerative colitis, Crohn'sdisease, atopic dermatitis, rapidly progressive glomerulonephritis, orsystemic inflammatory response syndrome.
 78. A method of treatingcellular immune abnormality comprising causing the blood of the patientto come in contact with the selective leukocyte removal filter materialaccording to claim
 41. 79. The method according to claim 78, wherein thedisease is chronic or malignant rheumatoid arthritis, systemicerythematodes, Behcet's disease, idiopathic thrombo cytopenic purpura,autoimmune hepatitis, ulcerative colitis, Crohn's disease, atopicdermatitis, rapidly progressive glomerulonephritis, or systemicinflammatory response syndrome.